Field of the Invention
[0001] This invention relates to absorbent products and absorbent materials useful in the
manufacture of absorbent products, such as sanitary napkins, pantyliners, incontinence
devices, diapers, and to such related absorbent products.
Background of the Invention
[0002] Absorbent products such as sanitary napkins and diapers typically comprise an absorbent
core, a liquid impermeable backing material, and a liquid permeable facing material.
The impermeable backing material prevents the bodily fluid from seeping out from the
absorbent core and staining the wearer's clothing. The absorbent core is also covered
with a facing material that,
inter alia, also serves to contain the absorbent core.
[0003] Normally, absorbent articles, such as pantyliners, sanitary napkins, baby and adult
diapers, as well as other adult incontinence devices, are formed by securing a liquid
impermeable film to an absorbent core and then attaching a facing material to the
impermeable film thereby securing the absorbent core between these two layers (
see,
e.g., Datta, et al., U.S. Patent No. 4,892,534). This process is both time consuming and expensive.
Moreover, if the facing is not in intimate contact with the core, the liquid on the
surface of the facing will puddle up and not penetrate through the facing but rather
run off the surface. This is highly undesirable behavior.
[0004] It is also undesirable to have the absorbent products move during use. The attachment
systems presently available often fail in this regard. During storage, the attachment
system's adhesive is covered with a release liner. Polyethylene or silicone coated
polyethylene paper is frequently used on the liners. Current adhesive attachment systems
consist of continuous coating of pressure-sensitive adhesives and a continuous silicone
coating on a release liner. Adhesives are normally thermoplastic rubber based and
hot melt coated, and are typically plasticized with oil. For various reasons, the
oil is an undesirable component of the adhesive. It imparts poor holding properties
to the adhesive and tends to move in the system by migrating from the adhesive to
the film, which is quite undesirable. The release liner on the attachment adhesive
is normally silicone or polyethylene coated paper. The resulting surface finish of
silicone coated papers is super smooth and the adhesive contact is 100% with the release
surface, which can be problematic. Depending on the type of silicone coating, the
silicone release system may cause the adhesive to be too easily released or too difficult
to release, which is undesirable. Thus, it is important that the release paper have
optimum release properties and at the same time make effective contact with the adhesive.
[0005] Many absorbent products optionally contain liquid absorbers, or odor absorbing materials
to mask the potential odor associated with the excreted bodily fluids. It has been
very difficult to immobilize such absorbents in disposable products. Frequently the
powder moves, which is very undesirable. In the past powders have been immobilized
on foams, or on continually coated pressure-sensitive adhesive surfaces to adhere
absorbent powder, and then inserted into the absorbent product. However, these approaches
are expensive because a great quantity of adhesive is required for immobilizing such
materials.
[0006] Despite the advances that have been made in the field of absorbent products such
as sanitary napkins, pantyliners, diapers, and incontinence products, there are still
needs to be addressed. For example, there is a need for absorbent products that have
better liquid transport properties and better odor and liquid absorbing properties.
There is a further need for absorbent products with more effective attachment systems
to give the user more security that the product will remain in place during routine
use. There is also a need for absorbent products that are manufactured using less
expensive and more efficient techniques. The present invention addresses these, as
well as other needs in the art.
Summary of the Invention
[0007] The present invention utilizes microfiber technology to provide absorbent products
that have good liquid transport properties, good liquid and odor absorbing properties,
good attachment systems, and at the same time are produced efficiently and cost effectively.
The microfibers of the invention comprise pressure-sensitive adhesives and/or plastic
polymers, depending on the purpose the microfiber coating is to serve.
[0008] In general, the invention relates to a variety of substrates coated with microfibers,
either pressure-sensitive adhesive microfibers or plastic polymer microfibers, at
a weight in the range of 1.70 to 67.81 g/m
2 (0.05 to 2 ounces/square yard); the weight typically depends on the particular substrate,
the particular microfibers, and the particular use of the substrate.
[0009] The pressure-sensitive adhesive microfibers may be coated onto substrates, such as
a facing, backing, or absorbent product to improve the absorbent products' liquid
transport properties, impart good liquid and odor absorbing properties, and good attachment
systems. Pressure-sensitive adhesives generally comprise an elastomeric component,
which comprises a linear or radial A-B-A block copolymer and a simple A-B block copolymer
or combinations thereof, wherein said A blocks are derived from styrene and said B
blocks are derived from alkenes or dienes; a resin component that comprises a solid
or liquid tackifier; and optionally a plasticizer.
[0010] The plastic polymer microfibers are used,
inter alia, for forming absorbent articles
in situ or for forming release liners with enhanced release properties. These plastic polymers
are selected from the group consisting of polyethylene, polypropylene, ethylene vinylacetate,
copolyesters, and plastic or thermoplastic rubber alloys.
[0011] In various embodiments, the microfibers typically have an average diameter of less
than 100µm (100 microns); however, this parameter also depends on the substrate, the
microfibers, and the particular use the microfiber coating is to serve. The substrate
may be an apertured, liquid permeable film; a liquid impermeable backing; an absorbent
panel or core; or an absorbent product. Many of the pressure-sensitive adhesive microfiber
coated substrates and plastic polymer microfiber coated substrates of the invention
may be used as components in a wide variety of absorbent products such as sanitary
napkins, pantyliners, incontinence devices, and diapers, without limitation. For example,
the attachment systems, components with enhanced liquid transport properties, and
the odor and liquid absorbing components disclosed herein have general application
to absorbent articles. Each of these embodiments, as well as others, are discussed
below.
[0012] In one embodiment of the invention, absorbent components having enhanced liquid transport
properties are presented. These components may be incorporated into a wide variety
of absorbent products. These components typically comprise a liquid permeable facing
material coated with pressure-sensitive adhesive microfibers. The coated facing material
is then placed adjacent to an absorbent core, with the coated side adjacent to the
core. The coating of pressure-sensitive microfibers enhances liquid transport properties
by placing the facing and absorbent core in intimate contact with each other. Products
incorporating these components may further comprise a liquid impermeable backing.
[0013] In another embodiment of the invention, pressure-sensitive adhesive microfibers may
be used to prepare liquid or odor absorbing components that may be incorporated into
a variety of absorbent products. Components such as a facing or backing material or
an absorbent core are coated with pressure-sensitive adhesive microfibers. The pressure-sensitive
adhesive microfibers are further coated with a liquid or odor absorbent.
[0014] In another embodiment of the invention, systems for attaching absorbent products
to a wearer's garment are disclosed. The attachment systems of the invention comprise
a substrate that is coated with pressure-sensitive adhesive microfibers on the side
of the substrate that faces the garment, and a release paper that protects the pressure-sensitive
adhesive coating up until the time the product is used. These attachment systems may
be used in a variety of absorbent products.
[0015] Another aspect of the invention relates to forming absorbent products
in situ. These absorbent products have plastic polymer microfiber coatings in place of standard
liquid permeable covers and/or liquid impermeable backings -- that is, the facing
and backing can be formed
in situ. For example, an absorbent core may be coated with plastic polymer microfibers on
the body-facing side of the absorbent core thereby forming a liquid permeable facing
over the core. In another example, an absorbent core may be sprayed on both sides
with plastic polymer microfibers, forming a liquid permeable facing surface on one
side of the absorbent core and a liquid impermeable backing surface on the opposite
side of the absorbent core.
[0016] The invention further embodies absorbent products for adhesive attachment to a wearer's
garment incorporating the aforementioned components. Such absorbent products comprise
a liquid impermeable backing, which may optionally be coated with pressure-sensitive
adhesive microfibers, and optionally have a liquid or odor absorbent immobilized on
it; a liquid permeable facing, which may optionally be coated with pressure-sensitive
adhesive microfibers, and optionally have a liquid or odor absorbent immobilized on
it; an absorbent core fixed between the facing and backing, which may optionally be
coated with pressure-sensitive adhesive microfibers, and optionally have a liquid
or odor absorbent immobilized on it; pressure-sensitive microfiber adhesive coating
on the body-facing surface of the backing that is contacted with the wearer's garment;
and a release paper covering over the pressure-sensitive adhesive.
Brief Description of the Drawings
[0017]
Figure 1 depicts a top and bottom view of an absorbent product that is formed in situ. The absorbent core 3 is being coated with microfibers 2 on the top surface, the surface that faces the user's body 4, using a spray nozzle 1 to form the liquid permeable facing. Fibers are also being sprayed on the bottom
5, the surface facing the wearer's garment, to form the liquid impermeable backing
5. The fibers are being sprayed onto the core's top and bottom surfaces using a nozzle
1. The spray nozzle method is only one method of spraying microfibers onto substrates.
The fibers sprayed using this method are typically spiral. Another method for spraying
microfibers is the melt-blown die technique, which sprays the microfibers straight;
this technique is preferable.
Figure 2 depicts an absorbent core 17 with a liquid impermeable backing 6 secured to the core's 17 bottom side. The top of the core 17 is being coated 9 with microfibers 8 thereby forming a liquid permeable facing 7 on the side of the core opposite the backing 6.
Figure 3 depicts an absorbent product, sanitary napkin, with a portion cut away to show the
core 12; the facing 10 and backing 11 are also depicted. The core 12 may be coated with microfibers as depicted in Figure 1 before it is contacted with
the facing 10. Alternatively, the facing 10 or backing 11 may be coated with microfibers before being contacted with the core 12. The microfibers sprayed on these various substrates may have a liquid or odor absorbent
immobilized on it before the sanitary napkin is assembled.
Figure 4 illustrates a sanitary napkin and its various components. The absorbent core 15 is fixed between the facing 18 and the backing 16. The backing 16 is coated with adhesive microfibers 13 and then covered with a release paper 14.
Detailed Description of the Preferred Embodiments
[0018] The present invention presents absorbent components, absorbent products, and materials
utilizing microfibers of pressure-sensitive adhesives and/or plastic polymers. These
pressure-sensitive adhesive and plastic polymer microfibers are formed using molten
spray technology. The resulting microfibers can be incorporated,
inter alia, into absorbent articles to enhance liquid transport properties, enhance liquid and
odor absorbing properties, and provide good attachment systems. The use of these pressure-sensitive
adhesives and plastic polymer microfibers produce absorbent products more efficiently
and economically than available methods.
[0019] In the context of this invention, the term "substrate" refers to any material that
can receive the pressure-sensitive adhesive or plastic polymer microfibers in accordance
with the invention; for example, a facing material, backing material, absorbent core,
or absorbent product, without limitation. As used herein, the terminology "facing
material" means that liquid-permeable component of the absorbent product that is in
contact with the user's skin when in use and covers at least one side of the absorbent
core. The terminology "backing material" means, as used herein, that portion of the
absorbent product that comes in contact with the wearer's clothing and covers at least
one side of the absorbent core. In the context of the invention, the terms "absorbent
core" or "absorbent panel" are used interchangeably, and mean that component of the
absorbent product fixed between the facing and backing materials to absorb bodily
fluid. The terminology "liquid absorbent," "odor absorbent," and "super absorbent"
refers to any material that is capable of absorbing liquid or odor. In the context
of this invention, a "plasticizer" means any material that gives an otherwise rigid
material, such as plastic, flexibility. Typically, plasticizers are used in pressure-sensitive
adhesives to give such adhesives wetness or tackiness. As used herein "elastomeric"
refers to thermoplastic materials that can be linear, radial, or branched molecular
structures that will repeatedly soften when heated and solidify when cooled, such
as acrylics, polyethylenes, polypropylenes, nylons, and thermoplastic rubbers as styrene
or isoprene and are a component of the pressure-sensitive adhesives of the invention.
In the context of this invention, "resin" refers to any solid or liquid organic material
of natural or synthetic origin that has an undefined melting point, and is generally
a polymer. As used herein, the term "plastic polymers" refers to thermoplastic polymer
materials such as polyethylene, polypropylene, ethylene vinylacetate, copolyesters,
and rubber or plastic alloys, and are used in forming,
inter alia, absorbent products
in situ and release liners. The term "microfibers," as used herein, refers collectively to
microfibers of pressure-sensitive adhesives and/or thermoplastics, unless otherwise
specified.
[0020] Fiberized pressure-sensitive adhesives and plastic polymers can be applied in hot
melt form using a spray fiberization method to form absorbent components and products
with good attachment properties, good liquid transport properties, and good odor and
liquid absorbing properties. Equipment is known in the art for forming microfibers
-- the microfiber nozzle spray (see Figures 1 and 2) or the melt blown die fiber formation
process. Both of these systems produce small diameter fibers having an average diameter
not greater than 100 µm (100 microns), the melt blown die process is preferred. In
both systems the molten microfibers are extruded through a microspray nozzle or through
a plurality of circular capillaries as filaments which are then processed through
a low or high velocity gas (i.e., air) stream that attenuates the filaments of molten
microfibers to reduce their diameter to a desired range for use in components of absorbent
products and absorbent products. These microfibers when still in a substantially molten
state or after some cooling, depending on the microfibers and desired use, are deposited
on a desired substrate and allowed to cool further.
[0021] The microfibers of the invention are employed in various manners in formulating absorbent
articles and materials used as component parts of absorbent articles, but the microfibers
generally preferably have certain properties. The materials preferably have a high
melt index, at least above 100, and more preferably above 1000; thus requiring a low
volume of air in the fiber making process. Such materials will be readily apparent
to those skilled in the art once armed with the present disclosure and may be used
without departing from the spirit of the invention. The microfibers are typically
microsized, have an average diameter of less than 100 µm (100 microns) so they do
not interfere with liquid transport. Where it is desired that the microfibers not
be affected by liquid, the microfibers will preferably be hydrophobic, (i.e., when
used to form a liquid impermeable backing material). The microfiber compositions preferably
have a high plasticity so that they do not flow out excessively once deposited on
a substrate. The microfibers preferably have a reasonable strength and the pressure-sensitive
adhesive microfibers, in particular, should have good adhesive properties.
[0022] Typically the plastic polymers are selected from the group consisting essentially
of polyethylene, polypropylene, ethylene vinylacetate, copolyesters, and plastic or
thermoplastic rubber alloys.
[0023] Typically the pressure-sensitive adhesives of the invention comprise an elastomeric
component, a resin component, and optionally a plasticizer to enhance wetness and
tackiness. Generally, the pressure-sensitive adhesives comprise linear or radial block
copolymers (A-B-A), simple block copolymers (A-B), or combinations thereof. The A-blocks
(end blocks) are derived, (i.e., polymerized), from styrene or styrene homologues,
and the B-blocks (center blocks) are derived from conjugated dienes, such as isoprene
or butadiene, or from lower alkenes, such as ethylene and butylene, and polymers and
copolymers thereof. Preferably, these pressure-sensitive adhesives typically comprise
styrene-isoprene-styrene (SIS) thermoplastic block copolymers having a low coupling
efficiency (15-65%) and less than 30% styrene.
[0024] In certain preferred embodiments, the pressure-sensitive adhesive microfibers will
have styrene-isoprene (SI) in the elastomer, and are tackified with a solid or liquid
resin, and may optionally be plasticized with a liquid resin or liquid rubber. Following
is a discussion of preferred embodiments with all parts expressed in parts per one
hundred parts by weight of the elastomeric component. The discussion of the pressure-sensitive
adhesive microfibers presents two general compositions, which may have varying ratios
of polymers. These two general compositions are for illustrative purposes and are
not intended to limit the invention.
[0025] In certain compositions, the elastomeric component preferably comprises from 10 to
100 parts of a linear or radial A-B-A block copolymer and 0 to 90 parts of a simple
A-B block copolymer, more preferably from 15 to 75 parts of a linear or radial A-B-A
block copolymer and 25 to 85 parts of a simple A-B block copolymer, more preferably
from 35 to 75 parts of a linear or radial A-B-A block copolymer and 25 to 65 parts
of a simple A-B block copolymer, more preferably from 50 to 90 parts of a linear or
radial A-B-A block copolymer and 10 to 50 parts of a simple A-B block copolymer, more
preferably, the elastomeric component will comprises from 60 to 80 parts of a linear
or radial A-B-A block copolymer and 20 to 40 parts of a simple A-B block copolymer,
the A blocks in the A-B block copolymer comprise from 5 to 50% by weight of the A-B
copolymer, more preferably between 10 to 40%, and more preferably between 10 to 35%;
and the total A-B and A-B-A copolymers comprise less than 50% styrene, more preferably
less than 40%, and more preferably less than 30%; and the resin component comprises
from 20 to 300 parts of a tackifier such as a solid or liquid resin or combinations
for said elastomeric component, more preferably from 100 to 140 parts of a tackifier
such as a solid or liquid resin or combinations thereof for said elastomeric component,
more preferably 50 to 120 parts of a solid or liquid resin or combinations thereof.
[0026] In other preferred embodiments, the elastomeric component will comprise from 15 to
45 parts of a linear or radial A-B-A block copolymer and 55 to 85 parts of a simple
A-B block copolymer, more preferably from 60 to 75 parts of the A-B block copolymer
and 25 to 40 parts of the A-B-A block copolymer, the A blocks in the A-B block copolymer
preferably constitute from 5 to 50% by weight of the A-B copolymer, more preferably
from 10 to 30%, from 5 to 20%, more preferably from 10 to 18%, and more preferably
from 12 to 16%.; and the total A-B and A-B-A copolymers comprise less than 30% styrene,
more preferably less than 25%, and more preferably less than 20%; and the resin component
preferably will comprise from 20 to 300 parts of a tackifier such as a solid or liquid
resin or combinations thereof, more preferably between 40 to 200, and more preferably
50 to 120 parts of a resin.
[0027] These and other pressure-sensitive adhesives suitable for practicing the claimed
invention are set forth in U.S. Patents Nos. 4,136,071, 4,080,348, and 4,759,754 issued
to Korpman on January 23, 1979, March 21, 1978, and July 26, 1988, respectively. Certain
components of the pressure-sensitive adhesives that may he used in practicing certain
specific aspects of the claimed invention are commercially available. For example,
Kraton RD 6043 is an SIS (styrene-isoprene-styrene) thermoplastic rubber having a
42% coupling efficiency and 220,000 M.W., and 17% styrene and is available from the
Shell Company. Kraton 1117 is a commercially available thermoplastic rubber having
a 65% coupling efficiency and 17% styrene. Kraton 1117 is a polystyrene-polyisoprene-polystyrene
thermoplastic elastomer sold by the Shell Company and is believed to comprise about
35 parts A-B and about 65 parts A-B-A.
[0028] The resin component consists essentially of tackifier resins for the elastomeric
component. In general any compatible conventional tackifier resin or mixture of such
resins may be used. Suitable resins are any compatible conventional tackifier resins
or mixtures thereof. These resins include, but are not limited to, hydrocarbon resins,
rosin and rosin derivatives, and polyterpenes. Wingtack Plus, for example, is a commercially
available resin. Wingtack Plus is a solid tackifier resin sold by Goodyear Tire and
Rubber Company consisting predominantly of polymerized structures derived from piperylene
and isoprene with a softening point of 95°C.
[0029] Plasticizers for pressure-sensitive adhesives include, but are not limited to, LIR
310, which is a liquid SI (styrene-isoprene) polymer available commercially from Arakawa
Chemical Company. Wingtack 10 is a liquid hydrocarbon tackifier of resin believed
to comprise synthetic polyterpene, and is used as a plasticizer for pressure-sensitive
adhesives. It has a softening point of 10°C, a viscosity of 20-40,000 cps at room
temperature and a molecular weight of about 450. It is available from Goodyear Chemical
Company.
[0030] Generally, the pressure-sensitive adhesive and the plastic polymer microfibers preferably
have an average diameter of less than 100 µm (100 microns), more preferably less than
50 µm (50 microns), and in certain embodiments more preferably between 0.5 to 25 µm
(microns). The microfibers' coating weight is preferably less than about 67.81 g/m
2 (2 ounces/square yard), in certain other embodiments more preferably 25.43 g/m
2 (0.75 ounces/square yard), in certain other embodiments more preferably between 10.17
to 20.34 g/m
2 (0.3 to 0.6 ounces/square yard), in yet other embodiments more preferably between
6.78 to 10.17 g/m
2 (0.2 to about 0.3 ounces/square yard), and in certain other embodiments more preferably
the coating has a weight of between 1.70 to 5.09 g/m
2 (0.05 to 0.15 ounces/square) yard. The particular variables are discussed below in
connection with various embodiments. The choice of the microfibers, coating weight
of the microfibers, and the diameter of the microfibers is typically dictated by the
particular use of the microfiber compositions.
[0031] The microfiber compositions used in the various embodiments of the invention may
also contain other materials, such as antioxidants, heat stabilizers, and ultraviolet
absorbers. Antioxidants that may be incorporated into the compositions, in particular
the pressure-sensitive adhesive compositions, include, but are not limited to, Sanotovar
A, which is a trademark for 2,5 diteriaryl amyl hydroquinone, ditertiary butyl cresol,
and Butyl Zimate, which is a trademark for zinc di-n-butyl-dithiocarbamate.
[0032] Fillers, such as zinc oxide, aluminum hydrate, clay, calcium carbonate, titanium
dioxide, carbon black, and others may also be incorporated into the microfiber compositions,
in particular the pressure-sensitive adhesive microfiber compositions, without departing
from the spirit of the invention. The various embodiments using pressure-sensitive
adhesive microfibers and/or plastic polymer microfibers are presented below.
[0033] In general, one aspect of the invention presents a substrate coated on at least one
surface with pressure-sensitive adhesive microfibers at a weight in the range of 1.70
to 67.81 g/m
2 (0.05 to 2 ounces/square yard) wherein said pressure-sensitive adhesive microfibers
comprise an elastomeric component, a resin component, and optionally a plasticizer;
and said microfibers have an average diameter of less than 100 µm (100 microns). Preferably,
the elastomeric component comprises a linear or radial A-B-A block copolymer and a
simple A-B block copolymer, wherein said A blocks are derived from styrene or styrene
homologues and said B blocks are derived from alkenes or dienes. The polymers of the
elastomeric component and their ratios have been discussed above; the resin component
and its ratio in the pressure-sensitive adhesive has also been discussed above.
[0034] In one more specific embodiment, the substrate is a liquid permeable facing material
10. The facing material
10 is coated with pressure-sensitive adhesive microfibers on the side to be contacted
with the core 12. These microfibers have a weight from 1.70 to 13.56 g/m
2 (0.05 to 0.4 ounces/square yard); preferably the coating weight is 8.48 g/
2/(0.25 ounces/square yard), more preferably 6.10 g/m
2 (0.18 ounces/square yard), and more preferably 3.39 g/m
2 (0.10 ounces/square yard). The average diameter of the pressure-sensitive adhesive
microfibers is less than 50 µm (50 microns), more preferably between 1 to 25 µm (microns).
[0035] A facing material
10 coated with a layer of pressure-sensitive adhesive microfibers can be used to produce
an absorbent product with enhanced liquid transport properties. The pressure-sensitive
adhesive microfiber coated surface (underside of
10) of the facing material
10 is placed adjacent to an absorbent core
12 or panel, and the adhesive fibers serve to maintain the facing in intimate contact
with the core while not obstructing passage of fluid through the facing to the core
12. This structure allows the instantaneous transportation of liquids from the surface
of the facing material into the absorbent panel, leaving a substantially dry surface
on the body-facing surface of the facing material. This is highly desirable because
the user is then protected from the liquid caused by bodily exudate.
[0036] The coated liquid permeable facing material is incorporated into an absorbent product
using techniques known in the art. For example, the pressure-sensitive adhesive coated
side of the liquid permeable facing material is placed adjacent to the absorbent core
so that the two are in intimate contact, and then the outer rim of the facing material
is secured to the core.
[0037] Absorbent cores suitable for use with this invention may be formed from both absorbent
pulp fibers and resilient, synthetic fibers. The pulp fibers are generally formed
from fiberizing wood pulp sheets and generally comprise a combination of long and
short fibers. Suitable resilient, synthetic fibers include, but are not limited to,
polyester and polyethylene fibers. The relative amounts of pulp fibers and synthetic
fibers are not critical and can be determined by one skilled in designing such products,
in an effort to balance and achieve the desired properties of absorbency and resiliency.
The wood pulp fibers and synthetic fibers may be blended homogeneously throughout
the absorbent core, or the relative proportions of each may vary throughout the absorbent
core.
[0038] Absorbent cores may also be formed by other known techniques in which the fibers,
pulp and/or synthetic, are airlaid. To form the most stable core, the fibers in the
core are preferably bonded to one another. This may be done by heating the core to
a temperature above the melting temperature of the synthetic fibers so those fibers
fuse and bond to one another. Alternatively, bonding agents such as different thermo-bonding
fibers, hot melt spray adhesives, and bonding powders may be utilized. Specific means
that can be used to bond the fibers together include convection ovens, di-electric
ovens (radio frequency and microwave), infrared ovens, heated calendar rolls, forced
hot-air ovens, forced hot air during the panel forming process, and spray hot melt
adhesive during the panel forming process.
[0039] The liquid permeable facing provided on the absorbent structure of the present invention
should preferably be a film or fabric having a high degree of moisture permeability.
For example, the fabric may be polyester, polyethylene, polypropylene, bicomponent
fiber, nylon, rayon, or the like. The most suitable fabrics have unusually high elongation,
loft, softness and drape characteristics. Films that are perforated or noncontinuous
are also satisfactory. Though the cover is moisture permeable, it is preferably of
the type which after permeation of the moisture, prevents strike-back of the body
fluid when the absorbent structure is approaching saturation.
[0040] The liquid impermeable backing may be a liquid-impermeable polyolefin film, e.g.,
polyethylene or polyethylene terephthalate.
[0041] In another specific embodiment, pressure-sensitive adhesive microfibers may also
be used to immobilize liquid or odor absorbents on components of absorbent products,
such as a facing
10 or backing
11 material, or absorbent core
12. These coated components may then be incorporated into absorbent products as depicted
in Figures 3 and 4.
[0042] Heretofore, it has been difficult to immobilize particular liquid or odor absorbents
on a substrate (i.e., a facing or backing material or an absorbent core) and then
incorporate the substrate into absorbent products. Often these liquid or odor absorbers
are powders that tend to move. The pressure-sensitive adhesives can prevent this movement.
When used in this manner, the substrate receiving the pressure-sensitive adhesive
microfibers may be an absorbent panel
12, facing material
10, or backing material
11. It is preferred that the coating weight be less than 25.43 g/m
2 (0.75 ounces/square yard), more preferably between 11.87 g/m
2 (0.35 ounces/square yard) to 20.34 g/m
2 (0.6 ounces/square yard), and more preferably 13.56 g/m
2 (0.4 ounces/square yard). It is preferred that the average diameter of the pressure-sensitive
adhesive microfibers be less than 50 µm (50 microns), more preferably between 1 to
about 25 µm (microns). Absorbent products containing liquid or odor absorbents, as
described above, may be made according to methods known to those skilled in the art.
[0043] Generally, an absorbent powder is immobilized on a pressure-sensitive adhesive coated
facing material
10 before the side of the facing material coated with the pressure-sensitive adhesive
(underside of
10) is contacted with an absorbent core
12.
[0044] The absorbent powders or liquids that may be incorporated into the absorbent products
of the invention will be readily apparent to those skilled in the art. For example,
superabsorbents are well known in the art. One type of superabsorbent material provides
particles or fibers that may be described chemically as having a backbone of natural
or synthetic polymers with hydrophilic groups or polymers containing hydrophilic groups
being chemically bonded to the backbone or an intimate mixture therewith. Included
in this class of materials are such modified natural and regenerated polymers as polysaccharides
including, for example, cellulose and starch and regenerated cellulose which are modified
by being carboxylalkylated, phosphonoalkylated, sulfoalkylated, or phosphorylated
to render them highly hydrophilic. Such modified polymers may also be cross-linked
to improve their water-insolubility. Odor control agents suitable for practicing this
invention include, but are not limited to, baking soda and activated charcoal. Any
other liquid or odor absorbent materials known to those skilled in the art may be
used.
[0045] In another specific embodiment of the invention, the pressure-sensitive adhesive
microfiber coating is used as part of an attachment system
13 and
14 for attaching absorbent products to the user's garment. The substrate to receive
the coating
13 (
see e.g., Figures 3 and 4) in this embodiment is an absorbent product (
see Figure 4); the side facing the user's garment will receive the coating. The coating
13 comprises pressure-sensitive adhesive microfibers having a coating weight of between
6.78 to 33.91 g/m
2 (0.2 to 1 ounces/square yard), more preferably between 6.78 to 25.43 g/m
2 (0.2 to 0.75 ounces/square yard), and more preferably 8.48 g/m
2 (0.25 ounces/square yard) or less. The pressure-sensitive adhesive microfibers preferably
have an average diameter of less than 50 µm (50 microns), more preferably less than
30 µm (30 microns), and more preferably have an average diameter of between 1 to 25
µm (microns). In preferred embodiments, the substrate is an absorbent product, preferably
the pressure-sensitive adhesive microfiber coating
13 is on the garment facing surface of the absorbent product (
see Figure 4).
[0046] In another aspect of the invention, absorbent products formed
in situ using molten fiber spray technology are disclosed, rather than assembling the absorbent
product from the individual components -- facing, backing, and core (
see Figures 1 and 2). In this aspect of the invention, the microfibers are plastic polymers.
The plastic polymer microfibers may be sprayed
1 directly on an absorbent core
3, and may perform as a facing
4, backing
5, or both.
[0047] In one embodiment, only the facing fabric is eliminated (see Figure 2). Generally,
this approach requires that the absorbent core
17 be formed first and then contacted with a liquid impermeable barrier
6. The barrier
6, which may optionally be coated with pressure-sensitive adhesive microfibers before
being contacted with the core
17, and optionally have a liquid or odor absorbent immobilized on it, is preferably
laminated to one surface of the absorbent core
17 before a plastic polymer microfiber coating is placed on the opposite surface of
the core
7. The facing material
7 is then sprayed
9 directly on the absorbent core
17 by spraying melt blown plastic polymer microfibers
8 on the surface of the absorbent core
17 opposite the side that is in contact with the liquid impermeable barrier. In forming
the facing side
7, plastic polymer hydrophilic microfibers or a very thin layer of hydrophobic microfibers
8 are sprayed onto the absorbent core
17, which will permit liquid strike-through and deliver a nearly dry cover. Here the
plastic polymer microfibers should be cooled before coating the absorbent core.
[0048] In another embodiment of the invention, both the facing and the backing material
are eliminated (
see Figure 1). Generally, the backing
5 is replaced with plastic polymer hydrophobic microfibers
2 sprayed
1 on the absorbent panel. The facing is formed as described above.
[0049] The plastic polymers used in forming absorbent products
in situ are preferably selected from the group consisting of polyethylene, polypropylene,
ethylene vinylacetate, copolyesters, and plastic or thermoplastic rubber alloys, with
polyethylene preferred. The plastic polymer microfibers may be hydrophilic, hydrophobic,
or combinations thereof depending on the intended purpose. In forming the facing,
the molten microfibers should be cooled before being coated onto the substrate. The
coating weight is preferably between 6.78 to 33.91 g/m
2 (0.2 to 1 ounces/square yard), more preferably between 16.95 to 30.52 g/m
2 (0.5 to 0.9 ounces/square yard), and more preferably 20.34 to 27.12 g/m
2 (0.6 to 0.8 ounces/square yard). If the fibers are hydrophobic, the coating weight
should be between 6.78 to 25.43 g/m
2 (0.2 to 0.75 ounces/square yard), more preferably between 10.17 to 20.34 g/m
2 (0.3 to 0.6 ounces square yard), and more preferably between 6.78 to 13.56 g/m
2 (0.2 to 0.4 ounces/square yard). If hydrophilic fibers are used, the coating weight
should be between 6.78 to 33.91 g/m
2 (0.2 to 1 ounces/square yard), more preferably between 6.78 to 27.13 g/m
2 (0.2 to 0.8 ounces/square yard), and more preferably between 6.78 to 20.34 g/m
2 (0.2 to 0.6 ounces/square yard). If the fibers are a combination of hydrophobic and
hydrophilic fibers the same parameters as discussed in connection with the hydrophobic
fibers applies.
[0050] The plastic polymer microfibers preferably have an average diameter of 100 µm (100
microns) or less, more preferably between about 1 to 50 µm (microns), and more preferably
have an average diameter of between 0.5 µm (0.5 microns) to 25 µm (25 microns).
[0051] The plastic polymer microfibers described above may also be used to coat release
liners
14 or papers
14 used to cover adhesive attachment strips
13 on absorbent products (see Figure 4). Such release liners take advantage of the same
spray technology and provides a release liner with optimum release properties. The
melt blown plastic polymer microfibers
13 are sprayed on a paper substrate in a molten state, which delivers a somewhat coarse
surface with good release properties without the use of silicone reagents that are
currently used in the art. The plastic polymer is as described above, with polyethylene
preferred. In certain preferred embodiments, the plastic polymer microfiber coating
has a weight of 33.91 g/m
2 (1 ounces/square yard), and the microfibers have an average diameter of 100 µm (100
microns) or less. More preferably, the plastic polymer is polyethylene and has a coating
weight between 6.78 to 33.91 g/m
2 (0.2 to 1 ounces/square yard); more preferably the coating weight is between 13.56
to 30.52 g/m
2 (0.4 to 0.9 ounces/square yard), and more preferably between 22.04 to 27.13 g/m
2 (0.65 to 0.80 ounces/square yard), and the microfibers have an average diameter between
0.5 to 25 µm (microns). The polymer may also be compounded with the release agents
to further improve the release properties of the paper, such as Acrawax C which is
a synthetic wax having a melting point between 83°-143°C. Acrawax C is used as an
anti-tack agent and is available from Lenza Inc.
[0052] In another aspect of this invention, absorbent products incorporating the components
of the invention are disclosed. In one embodiment of the invention, an absorbent product
for adhesive attachment to a wearer's garment is presented (
see Figure 4). This product comprises a liquid impermeable backing
16; a liquid permeable facing
18; and an absorbent core
15 fixed between the backing
16 and facing
18. The backing and/or facing may optionally be coated with pressure-sensitive adhesive
microfibers before contacting with the absorbent core
15. The facing, backing, or absorbent core may further have a liquid or odor absorbent
immobilized on it.
[0053] In another embodiment of the invention, an absorbent product comprising an absorbent
core; a liquid impermeable backing; a facing material formed
in situ from plastic polymer microfibers; pressure-sensitive adhesive microfiber coating
on the side of the backing that is contacted with the wearer's garment, and a release
paper, as previously described is disclosed. Figures 1 and 4 are illustrative.
[0054] In another embodiment, an absorbent product comprising an absorbent core; a facing
and backing formed
in situ from plastic polymer microfibers; pressure-sensitive adhesive microfiber coating
on the side of the backing that is contacted with the wearer's garment; and a release
paper, as previously described is disclosed. Figures 2 and 4 are illustrative.
[0055] The parameters for these absorbent products, such as the particular microfibers used,
the coating weight, and size of the microfibers, is as discussed above in connection
with the various components of the invention.
EXAMPLES
Example 1
Forming Hydrophobic Fibers
[0056] Hydrophobic fibers may be formed from Petrothene low density polyethylene resin NA
601 which has a melt index of 2000. This product is commercially available from USI
Corporation. The fibers are formed by spraying the molten material through a spray
nozzle at 176.7°C (350°F), at low air consumption.
Example 2
Forming Hydrophilic Fibers
[0057] There are two ways to form hydrophilic fibers. The first approach is to spray surface
active dispersion on formed thermoplastic fibers. The other is to incorporate surface
active agent concentrate into the plastic pellets, DOW XU U1518.15, prior to fiber
spray. The surface active pellets are melted and mixed together with the fiber forming
plastic. A typical formulation would be:
Petrothene NA601 |
100 |
Dow XU 61518.15 |
25 |
[0058] The Petrothene is the fiber forming polyethylene which is mixed with Dow surface
Active Concentrate.
[0059] As in the case of hydrophobic fibers in Example 1, the hydrophilic fibers were formed
with a spray nozzle set-up at 176.7°C (350°F) and at a low air consumption.
Example 3
Forming Microfibers and Components Comprising Pressure-Sensitive Adhesives
[0060] The sprayed or melt blown pressure-sensitive adhesive microfibers consist of small
diameter adhesive fibers having an average diameter not greater than 100 µm (100 microns),
preferably 50 µm (50 microns), and more preferably having a diameter of from 1-25
µm (1-25 microns). These microfibers are made by extruding a molten, pressure-sensitive
adhesive through a micro-spray nozzle or through a plurality of fine, usually circular
capillaries as filaments into a low velocity gas (e.g., air) stream that attenuates
the filaments of the molten pressure-sensitive adhesive material to reduce their diameter
to the range stated above. The pressure-sensitive adhesive microfibers are carried
by the low velocity gas stream and are deposited on either a facing or backing, which
is then brought into contact with an absorbent panel.
[0061] The commonly used equipment for fiberization is the well-known melt blown die or
the spray nozzle set-up.
[0062] Some typical fiber forming hot melt pressure-sensitive adhesives are as follows (the
units are parts):
|
Formula 1 |
Formula 2 |
Formula 3 |
Kraton 1117 |
100 |
|
|
Kraton RP 6403 |
|
100 |
100 |
Wingtack Plus |
130 |
130 |
120 |
Wingtack 10 |
|
50 |
|
LIR 310 |
|
|
50 |
Butyl Zimate |
2 |
2 |
2 |
Santovar A |
1 |
1 |
1 |
[0063] The Kraton RD 6403 is a Shell SIS (Styrene-isoprene-styrene) thermoplastic rubber
having 42% coupling efficiency and 220,000 M.W. It has 17% styrene.
[0064] The Kraton 1117 is a commercially available thermoplastic rubber having 65% coupling
efficiency and 17% styrene.
[0065] Wingtack Plus is a solid hydrocarbon resin supplied by Goodyear Chemical Company
and used as a tackifier for thermoplastic rubber. It has a softening point of 95°C.
[0066] Wingtack 10 is a liquid hydrocarbon resin and is used as a plasticizer. It has a
softening point of 10°C.
[0067] LIR 310 is a liquid SI polymer available commercially from Kuraray Chemical Company,
and it is used in the formulation as a plasticizer.
[0068] The plastic polymer microfibers may be prepared using the same equipment. Examples
1 and 2 are illustrative of plastic polymer microfiber formulations.
Example 4
Components Coated with Pressure-Sensitive Adhesives for Adhering Liquid or Odor Absorbents
[0069] A typical pressure-sensitive adhesive formulation which can be formed into a microfiber
and which will have high adherence to the odor or liquid absorbent powder:
Kraton 1117 |
100 |
Wingtack Plus |
130 |
Butyl Zimate |
2 |
Santovar A |
1 |
[0070] The Kraton is a thermoplastic rubber which gives the internal strength to the pressure-sensitive
adhesive.
[0071] The Wingtack Plus is a hydrocarbon tackifier to give the adhesive tack properties.
[0072] Both Butyl Zimate and Santovar A are antioxidants for improved aging stability.
Example 5
Polyethylene Release Surface
[0073] A low density polyethylene resin available from USI, Petrothene NA 601, has been
successfully formed into molten fibers and deposited onto paper surface using the
molten fiber spray technology discussed in Example 1.
Example 6
Modified Polyethylene Release Surface
[0074] The polyethylene from Example 5 can be modified with a high melting wax before fiberization
like Acrawax C. An addition of 2-5% of the wax before fiberization will further enhance
the release properties.
Example 7
Pressure-sensitive Adhesive Microfibers Formed Without Plasticizer
[0075]
Kraton 1117 |
100 |
Wingtack Plus |
130 |
Butyl Zimate |
2 |
Santovar A |
1 |
[0076] The Kraton Rubber is tackified with Wingtack Plus and stabilized with two antioxidants;
Butyl Zimate and Santovar A.
Example 8
Plasticized Pressure-Sensitive Adhesive Microfiber Compositions
[0077]
Kraton 1117 |
100 |
Wingtack Plus |
130 |
Wingtack 10 |
50 |
Santovar A |
2 |
Butyl Zimate |
1 |
Kraton 1112 |
100 |
Arizona 7115 L |
120 |
Exxon ECR 143 H |
40 |
Butyl Zimate |
2 |
Santovar A |
1 |
[0078] The plasticized formulations are plasticized with liquid Wingtack 10 resin and Exxon
ECR 143H resin. Exxon ECR 143 H is a light color hydrogenated aliphatic resin. It
has a softening point of 12°C and a viscosity of 4212 cps at 50°C and an average molecular
weight of 462. It is available from Exxon Chemical Co. They could also be plasticized
with liquid elastomers. Arizona 7115 L is a terpene based tackifier with a softening
point of 115°C. It is available from Arizona Chemical Co. Kraton 1112 is a styrene-isoprene
(SI) polymer believed to be 14% styrene, 86% isoprene, and 40% di-block (SI). It has
a melt index of 23°C and is available from Shell Chemical Co.